Variable wavelength interference filter, optical module, and optical analyzer

ABSTRACT

A variable wavelength interference filter includes: a first reflective film disposed on a face of a first substrate facing a second substrate; a second reflective film disposed on a face of the second substrate facing the first substrate and the first reflective film; a first electrode disposed on the face of the first substrate; and a second electrode disposed on the face of the second substrate. The second substrate includes a movable portion on which the second reflective film is disposed and a connection maintaining portion maintaining the movable portion to be movable in a substrate thickness direction, the connection maintaining portion circumscribes the movable portion and is thinner than the movable portion, and the second electrode is disposed on a portion of the second substrate that is thicker than the connection maintaining portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional patent application of U.S. application Ser. No.13/372,946 filed Feb. 14, 2012 which claims priority to Japanese PatentApplication No. 2011-029490 filed Feb. 15, 2011, all of which areincorporated by reference herein in their entireties.

BACKGROUND

1. Technical Field

The present invention relates to a variable wavelength interferencefilter that selects and outputs light of a desired target wavelengthfrom incident light, an optical module that includes the variablewavelength interference filter, and an optical analyzer that includesthe optical module.

2. Related Art

Generally, a variable wavelength interference filter is known in whichreflective films are arranged on the opposing faces of two substrates soas that the reflective films face each other across a gap having apredetermined dimension (for example, see JP-A-7-286809).

In the variable wavelength interference filter disclosed inJP-A-7-286809, driving electrodes are arranged on the faces of twosubstrates so as to face each other, and, by applying driving voltagesto the driving electrodes, a gap interval can be adjusted in accordancewith an electrostatic attractive force. Here, one substrate includes alow-rigidity portion located on the periphery of the reflective film.The low-rigidity portion is formed to be thinner than that of the otherportions of the substrate and the driving electrode is also disposed onthis low-rigidity portion. In accordance with the transformation of thelow-rigidity portion, the flatness of the reflective film disposed onone substrate is secured. According to such a configuration, thevariable wavelength interference filter can transmit light of apredetermined wavelength in accordance with the gap interval.

Since the variable wavelength interference filter transmits light of adesired wavelength by adjusting the gap interval, high gap precision isrequired.

However, when the driving electrode is formed on the substrate, aninternal stress acts on the driving electrode in the facial direction (adirection extending along the substrate surface) of the drivingelectrode. The magnitude of the internal stress and the direction inwhich the stress acts are dictated based on the method of forming thedriving electrode as a film, the material of the film, and the like.Here, in a case where compressive stress acts on the driving electrodeformed on one substrate, the substrate is convexly bent toward the othersubstrate. On the other hand, in a case where tensile stress is appliedto the driving electrode formed on one substrate, the substrate isconvexly bent in a direction away from the other substrate.Particularly, since the low rigidity portion of the substrate has lowerrigidity than the other portions, in a case where the driving electrodeis formed on the low-rigidity portion, there is a concern that theamount of bending of the substrate may be large.

When the substrate is bent in accordance with the internal stress of theabove driving electrode, in an initial state in which no driving voltageis applied to the driving electrode, there is a problem in that bendingalso occurs in the reflective film so as to decrease the resolving powerof the variable wavelength interference filter.

SUMMARY

An advantage of some aspects of the invention is that it provides avariable wavelength interference filter, an optical module, and anoptical analyzer of which the resolving power is improved by decreasingthe bending occurring in the substrate.

An aspect of the invention is directed to a variable wavelengthinterference filter including: a first substrate that has transparency;a second substrate that faces the first substrate and has transparency;a first reflective film that is disposed on a face (surface) of thefirst substrate that faces the second substrate; a second reflectivefilm that is disposed on a face (surface) of the second substrate thatfaces the first substrate and faces the first reflective film across agap; a first electrode that is disposed on the face of the firstsubstrate that faces the second substrate; and a second electrode thatis disposed on the face of the second substrate that faces the firstsubstrate and faces the first electrode. The second substrate includes amovable portion on which the second reflective film is disposed and aconnection maintaining portion that maintains the movable portion so asto be movable in a substrate thickness direction, the connectionmaintaining portion is continuously formed so as to enclose (that is, toencircle or circumscribe) the movable portion and is formed to have athickness size smaller than that of the movable portion, and the secondelectrode is disposed on a portion of the second substrate that has athickness size larger than the connection maintaining portion.

Here, since the connection maintaining portion of the second substrateis formed to have a thickness smaller than that of the movable portion,the rigidity of the connection maintaining portion is lower than therigidity of the movable portion.

According to the above-described variable wavelength interferencefilter, the second electrode is disposed on a portion of the secondsubstrate that has a thickness size that is larger than that of theconnection maintaining portion of the second substrate. Thus, since thesecond electrode (film) is not formed in the connection maintainingportion, the internal stress of the second electrode does not act on theconnection maintaining portion. Accordingly, the bending of thesubstrate that occurs due to the internal stress can be decreased.Therefore, the bent state of the reflective film due to the bending ofthe substrate can be suppressed, whereby the resolving power of thevariable wavelength interference filter can be improved.

In the above-described variable wavelength interference filter, it ispreferable that the second electrode is disposed on the movable portion.

According to this configuration, since the second electrode is disposedon the movable portion that is maintained so as to be movable in thesubstrate thickness direction, even in a case where the electrostaticattractive force generated by applying voltages to the first electrodeand the second electrode is low, the movable portion can be moved to thefirst substrate side in accordance with the electrostatic attractiveforce. Accordingly, the voltage applied to each electrode may be low,whereby the power consumption of the variable wavelength interferencefilter can be suppressed.

In the above-described variable wavelength interference filter, it ispreferable that a support portion that is formed to have a thicknesssize larger than that of the connection maintaining portion and supportsthe connection maintaining portion is further included, the secondelectrode includes an inner electrode that is formed so as to enclose(circumscribe) the second reflective film and an outer electrode that isformed so as to enclose (circumscribe) the inner electrode, the innerelectrode is disposed on the movable portion, and the outer electrode isdisposed on the support portion.

According to this configuration, since the inner electrode of the secondelectrode is disposed on the movable portion, and the outer electrode ofthe second electrode is disposed on the support portion, the innerstress applied to the movable portion by the second electrode can belower than that of a case where both the electrodes are disposed on themovable portion. Therefore, the bending of the substrate can bedecreased even further.

In addition, since only the inner electrode of the second electrode isdisposed on the movable portion, the weight applied to the movableportion can be suppressed as compared to a case where the innerelectrode and the outer electrode are both disposed on the movableportion. Accordingly, since the inertia of the movable portion can below, the responsiveness of the reflective film at the time of drivingcan be improved.

In the above-described variable wavelength interference filter, it ispreferable that an anti-bending film that is disposed on a face locatedon a side opposite to the face of the second substrate that faces thefirst substrate is further included, and a direction in which internalstress acts in a facial direction of the anti-bending film and adirection in which internal stress acts in a facial direction of thesecond reflective film and the second electrode are the same.

According to this configuration, the anti-bending film is formed on theface located on the side opposite to the face of the second substratethat faces the first substrate, and the internal stress of theanti-bending film is formed in the same direction as the direction ofthe internal stress of the second reflective film or the secondelectrode. For example, the bending moment acting on the secondsubstrate based on the compressive stress of the anti-bending filmoffsets the bending moment caused by the compressive stress of thesecond reflective film or the second electrode that causes the secondsubstrate to be convexly bent toward the first substrate. Accordingly,the bending of the second substrate can be further decreased, wherebythe resolving power of the variable wavelength interference filter canbe improved further.

Another aspect of the invention is directed to an optical moduleincluding: the above-described variable wavelength interference filter;and a light receiving unit that receives test target light transmittedthrough the variable wavelength interference filter.

According to the above-described optical module, similarly to theabove-described variable wavelength interference filter, the bent stateof the second reflective film due to the bending of the second substrateis suppressed, whereby the resolving power of the variable wavelengthinterference filter can be improved. In accordance with this, light of adesired wavelength can be spectrally dispersed with high precision.Accordingly, by receiving light output from the variable wavelengthinterference filter by using the light receiving unit, the opticalmodule can measure a precise amount of a light component of a desiredwavelength included in the test target light.

Still another aspect of the invention is directed to an optical analyzerincluding: the above-described optical module; and an analysisprocessing unit that analyzes optical characteristics of the test targetlight based on the light received by the light receiving unit of theoptical module.

According to the above-described optical analyzer, since optical moduleincluding the above-described variable wavelength interference filter isincluded, the light amount can be measured with high precision. Thus, byperforming an optical analyzing process based on the measurement result,the optical characteristics can be precisely analyzed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a diagram showing a schematic configuration of a colorimetricapparatus according to a first embodiment of the invention.

FIG. 2 is a plan view showing a schematic configuration of an etalonaccording to the first embodiment.

FIG. 3 is a cross-sectional view showing a schematic configuration ofthe etalon according to the first embodiment.

FIG. 4 is a plan view of a first substrate according to the firstembodiment, as viewed from the second substrate side.

FIG. 5 is a plan view of the second substrate according to the firstembodiment, as viewed from the first substrate side.

FIG. 6 is a cross-sectional view showing a schematic configuration of anetalon according to a second embodiment of the invention.

FIG. 7 is a diagram showing a modified example according to theinvention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

First Embodiment

Hereinafter, a first embodiment according to the invention will bedescribed with reference to the drawings.

1. Schematic Configuration of Colorimetric Apparatus

FIG. 1 is a diagram showing a schematic configuration of a colorimetricapparatus (optical analyzer) including the variable wavelengthinterference filter according to the first embodiment of the invention.

The colorimetric apparatus 1, as shown in FIG. 1, includes a lightsource device 2 that emits light onto a test target A, a colorimetricsensor 3 (an optical module according to the embodiment of theinvention), and a control device 4 that controls the overall operationof the colorimetric apparatus 1. The colorimetric apparatus 1 is anapparatus that reflects light emitted from the light source device 2 onthe test target A, receives reflected test target light by using thecolorimetric sensor 3, and analyzes and measures the chromaticity of thetest target light, that is, the color of the test target A based on adetection signal output from the colorimetric sensor 3.

2. Configuration of Light Source Device

The light source device 2 includes a light source 21 and a plurality oflenses 22 (only one lens is shown in FIG. 1) and emits white light ontothe test target A. A collimator lens is included in the plurality oflenses 22, and the light source device 2 forms the white light emittedfrom the light source 21 to be parallel light by using the collimatorlens and emits the parallel light from a projection lens not shown inthe figure toward the test target A.

3. Configuration of Colorimetric Sensor

The colorimetric sensor 3, as shown in FIG. 1, includes: an etalon 5 (avariable wavelength interference filter according to the embodiment ofthe invention); a light receiving element 31 that receives lighttransmitted through the etalon 5 as a light receiving unit; and avoltage control unit 6 that changes the wavelength of light transmittedthrough the etalon 5. In addition, the colorimetric sensor 3 includes anincidence optical lens, which is not shown in the figure, guiding thereflection light (test target light) reflected by the test target A tothe inside of the colorimetric sensor 3 at a position facing the etalon5. In addition, in the colorimetric sensor 3, light of a predeterminedwavelength is spectrally dispersed out of the test target light incidentfrom the incidence optical lens from the etalon 5, and the spectrallydispersed light is received by the light receiving element 31.

The light receiving element 31 is configured by a plurality ofphotoelectric conversion elements and generates an electric signalcorresponding to the amount of received light. In addition, the lightreceiving element 31 is connected to the control device 4 and outputsthe generated electric signal to the control device 4 as a lightreception signal.

3-1. Configuration of Etalon

FIG. 2 is a plan view showing a schematic configuration of the etalon 5,and FIG. 3 is a cross-sectional view showing a schematic configurationof the etalon 5. In FIG. 3, it is assumed that the test target light isincident from the lower side of the figure.

The etalon 5, as shown in FIG. 2, is a plate-shaped optical memberhaving a square shape, and, for example, one side thereof is formed tohave a length of 10 mm. The etalon 5, as shown in FIG. 3, includes afirst substrate 51 and a second substrate 52. In this embodiment, forthese two substrates 51 and 52, a quartz crystal glass base formed fromSiO₂ (silicon dioxide) is used. In addition, the substrates 51 and 52,for example, may be formed from various kinds of glass such as sodaglass, crystalline glass, lead glass, potassium glass, borosilicateglass, and alkali-free glass, a quartz crystal, and the like. Among suchmaterials, as the material configuring the substrates 51 and 52, glassthat contains alkaline metal such as sodium (Na) or potassium (K) may beused. By forming the substrates 51 and 52 by using such glass, it ispossible to improve the adhesiveness between mirrors 56 and 57 andelectrodes 53 and 54, which will be described later, and the bondingstrength between the substrates 51 and 52. These two substrates 51 and52 are integrally formed by bonding together the bonding faces 513 and524 to be described later.

Between the first substrate 51 and the second substrate 52, a fixedmirror 56 as a first reflective film and a movable mirror 57 as a secondreflective film are disposed. Here, the fixed mirror 56 is fixed to aface of the first substrate 51 that faces the second substrate 52, andthe movable mirror 57 is fixed to a face 52A of the second substrate 52that faces the first substrate 51. In addition, the fixed mirror 56 andthe movable mirror 57 are arranged so as to face each other across aninter-mirror gap G.

In addition, between the first substrate 51 and the second substrate 52,a first electrostatic actuator 55A and a second electrostatic actuator55B, which are used for adjusting the dimension of the inter-mirror gapG between the fixed mirror 56 and the movable mirror 57, are disposed.

3-1-1. Configuration of First Substrate

The first substrate 51 is formed by processing a quartz crystal glassbase (SiO₂: silicon dioxide), for example, having a thickness of 500 μmthrough etching. More specifically, as shown in FIGS. 3 and 4, anelectrode forming groove 511 and a mirror fixing portion 512 are formedin the first substrate 51 through etching.

The electrode forming groove 511, in the plan view (hereinafter,referred to as an etalon plan view) viewed in the thickness direction ofthe etalon 5 as shown in FIG. 4, is formed in a circle-shape having theplanar center point as its center.

The mirror fixing portion 512, in the etalon plane view, is formed so asto protrude from the center portion of the electrode forming groove 511to the second substrate 52 side.

In the electrode forming groove 511, as shown in FIGS. 3 and 4, betweenthe outer peripheral edge of the mirror fixing portion 512 and the innercircumferential wall face of the electrode forming groove 511, anelectrode fixing face 511A having a ring shape is formed, and the firstelectrode 53 is formed in the electrode fixing face 511A. This firstelectrode 53 includes an inner first electrode 531 and an outer firstelectrode 532. The inner first electrode 531, in the etalon plan view (aplan view of the first substrate 51 viewed from the second substrate 52side) shown in FIG. 4, is formed in the shape of a ring having thecenter of the fixed mirror 56 as its center point. The outer firstelectrode 532, in the etalon plan view, on the same axis as that of theinner first electrode 531, is formed in the shape of a letter “C” havinga diameter size larger than that of the inner first electrode 531.

Here, the first electrode 53 is not particularly limited as long as ithas conductivity and can generate an electrostatic attractive forcebetween the first electrode 53 and the second electrode 54 by applying avoltage between the second electrode 54 of the second substrate 52 andthe first electrode 53. In this embodiment, ITO (Indium Tin Oxide) isused as the material of the first electrode 53. Alternatively, a metallamination body of an Au/Cr film (a film formed by using a chromium filmas a base and a gold film is formed thereon) or the like may be used.

In addition, on the upper face of the first electrode 53, an insulatingfilm 58 is formed. As the material of the insulating film 58, SiO₂, TEOS(Tetra Ethoxy Silane), or the like can be used, and, particularly, it ispreferable to use SiO₂ that has the same optical characteristics asthose of the glass substrate forming the first substrate 51. In a casewhere SiO₂ is used as the insulating film 58, there is no reflection oflight and the like between the first substrate 51 and the insulatingfilm 58, and thus, for example, as shown in FIG. 3, after the firstelectrode 53 is formed on the first substrate 51, the insulating film 58may be formed on the entire face of the first substrate 51 that facesthe second substrate 52 side. In addition, this insulating film 58 is afilm used to prevent leakage due to discharge between the firstelectrode 53 and the second electrode 54 or the like and may beconfigured by a film that does not have transparency. In such a case,the insulating film 58 located on the mirror fixing face 512A may beeliminated.

From a part of the outer peripheral edge of the inner first electrode531, in the etalon plan view shown in FIG. 4, an inner first electrodelead-out portion 531L is formed so as to extend toward the upper leftside of the etalon 5. In addition, from a part of the outer peripheraledge of the outer first electrode 532, in the etalon plan view, an outerfirst electrode lead-out portion 532L is formed so as to extend towardthe lower right side of the etalon 5. At the tip ends of the inner firstelectrode lead-out portion 531L and the outer first electrode lead-outportion 532L, an inner first electrode pad 531P and an outer firstelectrode pad 532P are formed, and the inner first electrode pad 531Pand the outer first electrode pad 532P are connected to the voltagecontrol unit 6 (see FIG. 1). In order to drive the electrostaticactuators 55A and 55B, voltages are applied to the inner first electrodepad 531P and the outer first electrode pad 532P by the voltage controlunit 6 (see FIG. 1).

The mirror fixing portion 512, as described above, on the same axis asthat of the electrode forming groove 511, is formed in a cylindricalshape having a smaller size diameter than that of the electrode forminggroove 511. In addition, in this embodiment, as shown in FIG. 3,although an example is illustrated in which the mirror fixing face 512Aof the mirror fixing portion 512 that faces the second substrate 52 isformed to be closer to the second substrate 52 than the electrode fixingface 511A, the invention is not limited thereto. The height positions ofthe electrode fixing face 511A and the mirror fixing face 512A areappropriately set based on the size of the inter-mirror gap G betweenthe fixed mirror 56 fixed to the mirror fixing face 512A and the movablemirror 57 formed in the second substrate 52, the dimension between thefirst electrode 53 and the second electrode 54, and the thickness sizeof the fixed mirror 56 or the movable mirror 57, and are not limited tothe above-described configuration. For example, in a case where thethickness size is increased by using the dielectric multi-layer mirroras the mirrors 56 and 57, a configuration in which the electrode fixingface 511A and the mirror fixing face 512A are formed on the same face ora configuration in which a mirror fixing groove having a cylindricalgroove shape is formed in the center portion of the electrode fixingface 511A, and the mirror fixing face 512A is formed on the bottom faceof the mirror fixing groove, or the like may be employed. In addition,it is preferable to design the groove depth of the mirror fixing face512A of the mirror fixing portion 512 taking into account the wavelengthband for which light is transmitted through the etalon 5.

In addition, the fixed mirror 56, which has a circular shape having adiameter of about 3 mm, is fixed to the mirror fixing face 512A. Thisfixed mirror 56 is a mirror that is formed by a dielectric multi-layerfilm formed from TiO₂—SiO₂ based materials in which a TiO₂ film and aSiO₂ film are laminated and is formed on the insulating film 58 formedon the mirror fixing face 512A by using a sputtering technique or thelike.

Furthermore, in this embodiment, although an example is illustrated inwhich the dielectric multi-layer film formed from TiO₂—SiO₂ basedmaterials is used as the fixed mirror 56, a configuration may beemployed in which a mirror of an Ag alloy single layer that can coverthe entire visible region as the wavelength region which can bespectrally dispersed, is used.

Here, a portion of the first substrate 51, in which the electrodeforming groove 511 and the mirror fixing portion 512 are not formed, isa bonding face 513 of the first substrate 51. On the insulating film 58formed on the bonding face 513, as shown in FIG. 3, a first bonding film514 used for bonding is formed. As the first bonding film 514, a plasmapolymer film using polyorganosiloxane as its main material or the likecan be used.

3-1-2. Configuration of Second Substrate

The second substrate 52 is formed by processing a quartz crystal glassbase (SiO₂: silicon dioxide), for example, having a thickness of 200 μmthrough etching.

In addition, in the second substrate 52, as shown in FIGS. 2 and 3, inthe etalon plan view, a displacement portion 521 having a circle shapethat has the substrate center point as its center is formed. Thisdisplacement portion 521 includes a cylinder-shaped movable portion 522and a connection maintaining portion 523 that has the same axis as thatof the movable portion 522 and maintains the movable portion 522.

This displacement portion 521 is formed by forming a groove in a flatplate-shaped glass base, which is a material forming the secondsubstrate 52, through etching. In other words, the displacement portion521 is formed by forming a circular ring-shaped groove portion 523A usedfor forming the connection maintaining portion 523 in a face of thesecond substrate 52 that does not face the first substrate 51 throughetching.

The movable portion 522 is formed to have a thickness size larger thanthat of the connection maintaining portion 523. For example, in thisembodiment, the movable portion 522 is formed to have a thickness sizeof 200 μm that is the same as the thickness size of the second substrate52. In addition, the movable portion 522 includes a movable face 522Aparallel to the mirror fixing portion 512 on a face 52A located on aside facing the first substrate 51, and the movable mirror 57 is fixedto the movable face 522A.

Here, this movable mirror 57 is a mirror having the same configurationas that of the above-described fixed mirror 56, and, for example, has acircular shape having a diameter of 3 mm, and a mirror of a dielectricmulti-layer film that is formed from a TiO₂—SiO₂ based material is used.

In the movable face 522A of the movable portion 522, as shown in FIGS. 3and 5, a second electrode 54 having a double ring shape that faces thefirst electrode 53 with a predetermined gap interposed therebetween isformed. This second electrode 54 includes an inner second electrode 541as an inner electrode formed so as to enclose the movable mirror 57 andan outer second electrode 542 that is formed so as to enclose the innersecond electrode 541 as an outer electrode. Here, the firstelectrostatic actuator 55A is configured by the inner first electrode531 and the inner second electrode 541, and the second electrostaticactuator 55B is configured by the outer first electrode 532 and theouter second electrode 542.

The inner second electrode 541, in the etalon plan view (a plan view ofthe second substrate 52 viewed on the first substrate 51 side) shown inFIG. 5, is formed in a ring shape having the center of the movablemirror 57 as its center point. The outer second electrode 542, on thesame axis as that of the inner second electrode 541 in the etalon planview, is formed in a ring shape having a larger size diameter than thatof the inner second electrode 541 and is connected to the inner secondelectrode 541.

In addition, a metal-laminated body formed from ITO (Indium Tin Oxide)or an Au/Cr film is used for the second electrode 54.

In addition, from a part of the outer peripheral edge of the outersecond electrode 542, one pair of second electrode lead-out portions542L are formed to extend in opposite directions, and a second electrodepad 542P is formed at the tip end of the second electrode lead-outportion 542L. More specifically, the second electrode lead-out portion542L, in the etalon plan view shown in FIG. 5, extends toward the upperleft side and the lower right side of the etalon 5 and is formed to havepoint-symmetry with respect to the planar center of the second substrate52.

In addition, the second electrode pad 542P, similarly to the inner firstelectrode pad 531P and the outer first electrode pad 532P, is connectedto the voltage control unit 6, and, when the electrostatic actuator 55Ais driven, a voltage is applied to the second electrode pad 542P.

The connection maintaining portion 523 is a circle-shaped diaphragmenclosing (encircling or circumscribing) the periphery of the movableportion 522, and, for example, is formed to have a thickness size of 30μm that is thinner than the thickness size of the movable portion 522.Here, in the connection maintaining portion 523, as shown in FIG. 3, afilm such as the second electrode 54 is not formed, and internal stressof the film does not act on the connection maintaining portion 523.

In a face 52A of the second substrate 52, an area facing the bondingface 513 of the first substrate 51 is a bonding face 524 of the secondsubstrate 52. In this bonding face 524, similarly to the bonding face513 of the first substrate 51, a second bonding film 525 usingpolyorganosiloxane as its main material is disposed.

3-2. Configuration of Voltage Control Unit

The voltage control unit 6 controls the voltages to be applied to firstand second electrodes 53 and 54 of the electrostatic actuators 55A and55B based on a control signal that is input from the control device 4.

4. Configuration of Control Device

The control device 4 controls the overall operation of the colorimetricapparatus 1. As the control device 4, for example, a general-purposepersonal computer, a portable information terminal, acolorimetry-dedicated computer, or the like may be used.

As shown in FIG. 1, the control device 4 includes a light source controlunit 41, a colorimetric sensor control unit 42, a colorimetricprocessing unit 43 (analysis processing unit), and the like.

The light source control unit 41 is connected to the light source device2. In addition, the light source control unit 41 outputs a predeterminedcontrol signal to the light source device 2, for example, based on asetting input from a user and emits white light having a predeterminedbrightness level from the light source device 2.

The colorimetric sensor control unit 42 is connected to the colorimetricsensor 3. In addition, the colorimetric sensor control unit 42 sets thewavelength of the light to be received by the colorimetric sensor 3, forexample, based on a setting input from a user and outputs a controlsignal for the purpose of detecting the amount of received light havingthe wavelength to the colorimetric sensor 3. As a result, the voltagecontrol unit 6 of the colorimetric sensor 3 sets the voltages applied tothe electrostatic actuators 55A and 55B based on the control signal suchthat light having the wavelength desired by a user is transmitted.

The colorimetric processing unit 43 changes the inter-mirror gap of theetalon 5 by controlling the colorimetric sensor control unit 42, therebychanging the wavelength of light transmitted through the etalon 5. Inaddition, the colorimetric processing unit 43 acquires an amount oflight transmitted through the etalon 5 based on a reception signal inputfrom the light receiving element 31. Then, the colorimetric processingunit 43 calculates the chromaticity of light reflected by the testtarget A based on the amount of received light of each wavelengthacquired as above.

5. Operation and Advantage of First Embodiment

According to the above-described etalon 5 of the first embodiment, thefollowing advantages are acquired.

Since the second electrode 54 is disposed on a portion of the secondsubstrate 52 other than the connection maintaining portion 523, theinternal stress of the second electrode 54 does not act on theconnection maintaining portion 523. Accordingly, the connectionmaintaining portion 523 having the low rigidity of the second substrate52 can be prevented from being influenced by the internal stress of thesecond electrode 54, whereby the bending of the second substrate 52 thatoccurs due to the internal stress can be decreased. Therefore, the bentstate of the reflective film due to the bending of the substrate can besuppressed, whereby the resolving power of the etalon 5 can be improved.

In the connection maintaining portion 523, there is no formation of afilm including the second electrode 54, and accordingly, the diaphragmthat is the connection maintaining portion 523 enclosing the peripheryof the movable portion 522 may easily bend, whereby the driving controlof the diaphragm at the time of applying driving voltages to the firstelectrode 53 and the second electrode 54 can be easily performed.

In addition, since the first electrode 53 is covered with the insulatingfilm 58, current leakage between the first electrode 53 and the secondelectrode 54 due to discharge or the like can be reliably prevented,whereby desired electric charge according to the set voltages can bemaintained in the first electrode 53 and the second electrode 54.Accordingly, the gap G interval between the fixed mirror 56 and themovable mirror 57 can be controlled with high precision, whereby lightof a desired wavelength can be satisfactorily emitted from the etalon 5.

Furthermore, since application voltages for each of the electrostaticactuators 55A and 55B can be controlled by the voltage control unit 6,setting of the gap can be performed with high precision.

Second Embodiment

Hereinafter, a second embodiment according to the invention will bedescribed with reference to FIG. 6.

The second electrode 54 included in the above-described etalon 5according to the first embodiment is formed in the movable portion 522.

In contrast to this, in the second electrode 54 included in the etalonof this embodiment, an inner second electrode 541 is formed on the innerside of a connection maintaining portion 523, that is, on a movableportion 522, and an outer second electrode 542 is formed on the outerside of a connection maintaining portion 523. In addition, on a face 52Bof the second substrate 52 located on a side opposite to the firstsubstrate 51, an anti-bending film 59 that has transparency is disposed.

In addition, in the description presented below, the same referencenumerals are assigned to the same constituent elements as those of thefirst embodiment, and the description thereof will not be repeated.

FIG. 6 is a cross-sectional view showing a schematic configuration ofthe etalon of this embodiment.

In this etalon 5A, a displacement portion 521 of the second substrate52, as shown in FIG. 6, includes a movable portion 522, the connectionmaintaining portion 523 that maintains the movable portion 522, and asupport portion 526 that supports the connection maintaining portion 523from the outer side of the connection maintaining portion 523.

The movable portion 522 and the connection maintaining portion 523 areconfigured similarly to those of the first embodiment. In other words,the connection maintaining portion 523 is a circle-shaped diaphragmenclosing (encircling or circumscribing) the periphery of the movableportion 522, and the movable portion 522 is formed so as to have athickness size larger than the connection maintaining portion 523.

The support portion 526 is a portion of the second substrate 52 that islocated on the outer side of the connection maintaining portion 523 andis configured by a portion that faces the electrode fixing face 511A ofthe first substrate 51. This support portion 526 is formed to have athickness size larger than that of the connection maintaining portion523, and, for example, the thickness size thereof is formed to be 200 μmthat is the same size as the thickness size of the second substrate 52.

A second electrode 54 includes a ring-shaped inner second electrode 541disposed on the movable portion 522 and a ring-shaped outer secondelectrode 542 disposed on the support portion 526 and enclosing theperiphery of the connection maintaining portion 523. In correspondencewith the second electrode 54, a first electrode 53 is disposed at aposition at which an inner first electrode 531 faces the inner secondelectrode 541, and at a position at which an outer first electrode 532faces an outer second electrode 542.

An anti-bending film 59 is formed at a position (the upper face of themovable portion 522 and the upper face of the support portion 526) onthe face 52B of the second substrate 52 covering the movable mirror 57and the second electrode 54. The anti-bending film 59 is configured by amaterial having the same refractive index as that of the secondsubstrate 52, and, in this embodiment, is configured by a quartz crystalglass material (SiO₂: silicon dioxide) that is the same as that of thesecond substrate 52. This anti-bending film 59 decreases the bending ofthe second substrate 52 that convexly bends toward the first substrate51 due to internal stress (in this embodiment, compressive stress) thatacts in the facial direction of the movable mirror 57 and the secondelectrode 54 when the movable mirror 57 and the second electrode 54 areformed as films on a face of the second substrate 52 that faces thefirst substrate 51.

In other words, when the second electrode 54 or the movable mirror 57 isformed as a film on the face 52A of the second substrate 52 that facesthe first substrate 51, the second substrate 52 tends to be bent towardthe first substrate 51 side due to the internal stress (compressivestress) of the second electrode 54 or the movable mirror 57.

Here, in a case where the movable mirror 57 is a dielectric multi-layerfilm that is formed from a TiO₂—SiO₂ based material, the sum of theproducts of the internal stress and the thickness size of each layer(the TiO₂ layer and the SiO₂ layer) of the movable mirror 57 and thearea of each layer in the plan view acts on the second substrate 52 asbending moment. When the bending moment of the movable mirror 57 actingon the second substrate 52 is M1, the internal stress of the entiremovable mirror 57 is σ1, the total thickness size of the movable mirror57 is T1, the area of the movable mirror 57 in the etalon plan view isS1, the internal stress of each TiO₂ layer is σ11, the thickness size ofthe TiO₂ layer is T11, the layer number of the TiO₂ layers is N11, theinternal stress of each SiO₂ layer is σ12, the thickness size of theSiO₂ layer is T12, and the layer number of SiO₂ layers is N12, thefollowing Equation (1) is satisfied.M1∝σ1×T1×S1=(σ11×T11×N11×S1)+(σ12×T12×N12×S1)  (1)

In this embodiment, the internal stress of the movable mirror 57, thesecond electrode 54, and the anti-bending film 59 may be set so as to becompressive stress such that the internal stress σ1 of the entiremovable mirror 57 is compressive stress, for example, even in a casewhere the internal stress of the TiO₂ layer and the internal stress ofthe SiO₂ layer of the movable mirror 57 are tensile stress andcompressive stress. Then, the bending moment M1 acquired by usingEquation (1) described above acts as a force for bending the secondsubstrate 52 from the movable mirror 57.

Similarly, when the bending moment of the second electrode 54 acting onthe second substrate 52 is M2, the internal stress of the secondelectrode 54 is σ2, the thickness size of the second electrode 54 is T2,and the area of the second electrode 54 is S2 in the etalon plan view,the following Equation (2) is satisfied.M2∝σ2×T2×S2  (2)

Then, the bending moment M2 acquired by using Equation (2) describedabove acts as a force for bending the second substrate 52 from thesecond electrode 54.

As described above, in a case where the internal stress σ1 of themovable mirror 57 and the internal stress σ2 of the second electrode 54are compressive stress applied in the same direction, a bending momentM3 as represented in the following Equation (3) acts on the secondsubstrate 52 so as to be a force for bending the second substrate 52 tothe first substrate 51 side.M3=M1+M2  (3)

The anti-bending film 59 is a film disposed for negating the bendingmoment M3, which is acquired by using Equation (3) described above,acting on the second substrate 52 and has internal stress (compressivestress) applied in the same direction as that of the internal stress(compressive stress) acting in the facial direction of the secondelectrode 54 and the movable mirror 57. In addition, the anti-bendingfilm 59, as described above, is disposed on the face 52B located on aside opposite to the face 52A on which the second electrode 54 and themovable mirror 57 are disposed. Accordingly, the bending moment actingon the second substrate 52 in accordance with the internal stress of theanti-bending film 59 works in a direction in which the second substrate52 is separated away from the first substrate 51.

Here, when the bending moment of the anti-bending film 59 acting on thesecond substrate 52 is M4, the internal stress (compressive stress) ofthe anti-bending film 59 is σ4, the thickness size of the anti-bendingfilm 59 is T4, and the area of a portion overlapping the gap formingportion in the etalon plan view is S4, a bending moment M4 acquired bythe following Equation (4) acts on the second substrate 52. Thus, byforming the anti-bending film 59 such that the bending moment M4 has therelation of the following Equation (5), the bending moment M3 acting onthe second substrate 52 is negated by the second electrode 54 and themovable mirror 57, whereby the bending of the second substrate 52 can becleared.M4∝σ4×T4×S4  (4)M4=M3  (5)

According to the above-described etalon 5 of the second embodiment, inaddition to the above-described advantages of the first embodiment, thefollowing advantages are acquired.

Since only the inner second electrode 541 out of the second electrodes54 is disposed on the movable portion 522, the weight applied to themovable portion 522 can be suppressed compared to a case where the innersecond electrode 541 and the outer second electrode 542 of the secondelectrode 54 are both disposed on the movable portion 522. Thus, sincethe inertia of the movable portion 522 can be low, the responsiveness ofthe movable mirror 57 at a time when it is driven can be improved.

In addition, since the inner second electrode 541 is disposed on themovable portion 522, and the outer second electrode 542 is disposed onthe support portion 526, the internal stress of the second electrode 54acting on the movable portion 522 can be lower than that of the casewhere both the electrodes 541 and 542 are disposed on the movableportion 522. Accordingly, the bent state of the movable portion 522 canbe prevented, whereby the flatness of the movable mirror 57 can beimproved.

Here, since the anti-bending film 59 is formed on the side of the secondsubstrate 52 that is located opposite to the side facing the firstsubstrate 51, and, when the film is formed, compressive stress isapplied in the facial direction of the anti-bending film 59.Accordingly, in accordance with the compressive stress acting in thefacial direction of the anti-bending film 59, the second substrate 52 isconvexly bent toward the side opposite to the first substrate 51, andaccordingly, the convex bending of the second substrate 52 toward thefirst substrate 51 can be decreased.

In addition, the bending moment M3 acting on the second substrate 52 atthe time of forming the second electrode 54 and the movable mirror 57 inthe second substrate 52 as films is set such as to be the same as thebending moment M4 acting on the second substrate 52 at the time offorming the anti-bending film 59 on the second substrate 52 (seeEquation (5)). Accordingly, the bending moment M3 acting on the secondsubstrate 52 at the time of forming the second electrode 54 and themovable mirror 57 as films in the second substrate 52 can be negated bythe bending moment M4 acting on the second substrate 52 of theanti-bending film 59. Accordingly, the bending of the second substrate52 in the initial state can be reliably prevented, the gap G intervalbetween the fixed mirror 56 and the movable mirror 57 can be set withhigh precision, whereby the resolving power of the etalon 5A can beimproved further.

Since the anti-bending film 59 is formed from the quartz crystal glassmember (SiO₂) that is the same optical characteristics as those of thesecond substrate 52, the light incident to the second substrate 52 canbe prevented from being reflected at the bonding face between theanti-bending film 59 and the second substrate 52. Accordingly, light ofa specific wavelength can be well transmitted from the incident light.

In addition, since the thickness size of the movable portion 522 isincreased in accordance with the formation of the anti-bending film 59,the rigidity of the movable portion 522 is increased so as to be noteasily bent. Accordingly, the bending of the movable mirror 57 can beprevented more reliably.

In the connection maintaining portion 523 of the second substrate 52,formation of a film including the second electrode 54 is not performed.Accordingly, even in a case where the balance of the stress collapsesdue to the unbalance of the thickness or the internal stress of thesecond electrode 54, the movable mirror 57, and the anti-bending film59, the internal stress due to the film formation does not act on theconnection maintaining portion 523. Accordingly, the bending of thesecond substrate 52 due to the internal stress of the second electrode54, the movable mirror 57, and the anti-bending film 59 can besuppressed to be minimal.

Modification of Embodiment

The invention is not limited to the above-described embodiments, and,modifications, improvements, and the like in the scope attaining theobject of the invention belong thereto.

In the above-described first embodiment, the inner second electrode 541and the outer second electrode 542 configuring the second electrode 54are disposed on the movable portion 522, and, in the above-describedsecond embodiment, the inner second electrode 541 is disposed on themovable portion 522, and the outer second electrode 542 is disposed onthe support portion 526. However, the invention is not limited thereto.For example, as shown in FIG. 7, in the etalon 5B, the inner secondelectrode 541 and the outer second electrode 542 may both be disposed onthe support portion 526.

In addition, in the above-described embodiments, although the firstelectrode 53 and the second electrode 54 are formed in a double-ringshape, the shape of the electrodes 53 and 54 are not limited thereto.The first electrode 53 and the second electrode 54 may be in the shapeof a single ring or a multiple ring shape having three rings or more.

In the above-described second embodiment, although the second electrode54, the movable mirror 57, and the anti-bending film 59 are formed asfilms on the second substrate 52 such that the internal stress actingthereon is compressive stress, they may be formed as films so as toallow tensile stress to act thereon. Even in such a case, the secondelectrode 54, the movable mirror 57, and the anti-bending film. 59 maybe formed such that the direction of the internal stress acting thereonis the same.

In the above-described second embodiment, although the anti-bending film59 is formed at a position covering the movable mirror 57 and the secondelectrode 54 on the face 52B of the second substrate 52 that is locatedon the side opposite to the first substrate 51, the anti-bending film 59may be formed on the entire face of the face 52B of the second substrate52 except for the connection maintaining portion 523.

In the above-described embodiments, although the insulating film 58 isformed only on the first electrode 53, the insulating film 58 may alsobe formed on the second electrode 54. In such a case, the secondelectrode 54, the movable mirror 57, the insulating film 58, and theanti-bending film 59 may be formed such that the direction of theinternal stress acting on the second electrode 54, the movable mirror57, the insulating film 58, and the anti-bending film 59 is the same,and the bending moment is balanced.

By also forming the insulating film 58 on the second electrode 54, thecurrent leakage between the first electrode 53 and the second electrode54 due to discharge or the like can be reliably prevented. Accordingly,a desired electric charge according to set voltages can be maintained inthe first electrode 53 and the second electrode 54. Therefore, the gapinterval between the fixed mirror 56 and the movable mirror 57 can becontrolled with high precision, whereby light of a desired wavelengthcan be emitted with high precision from the etalon 5.

In addition, in the above-described embodiments, although the fixedmirror 56 and the movable mirror 57 are formed in a circular shape, theshapes of the fixed mirror 56 and the movable mirror 57 are not limitedthereto. The fixed mirror 56 and the movable mirror 57 can be formed inshapes according to the use thereof and, for example, may be formed in arectangular shape.

In the above-described embodiments, although bonding is performed byusing the first bonding film 514 and the second bonding film 525 at thebonding faces 513 and 524, the invention is not limited thereto. Forexample, a configuration may be employed in which bonding is performedthrough so-called room-temperature activation bonding, in which bondingis performed by activating the bonding faces 513 and 524 without formingthe first bonding film 514 and the second bonding film 525 andoverlapping and pressing the activated bonding faces 513 and 524, andany bonding method may be used.

What is claimed is:
 1. A variable wavelength interference filtercomprising: a first substrate; a second substrate that faces the firstsubstrate; a first reflective film that is disposed between the firstsubstrate and the second substrate; a second reflective film that isdisposed between the first reflective film and the second substrate, agap existing between the first reflective film and the second reflectivefilm; a first electrode that is disposed between the first substrate andthe second substrate; a second electrode that is disposed between thefirst electrode and the second substrate; the second substrate having afirst portion and a second portion, the second portion being disposed soas to surround the first portion, the first portion having a first faceand a second face, and the second portion having a third face and afourth face, the first face continuing to the third face, the first facebeing opposed to the first substrate and the second face, the third facebeing opposed to the first substrate and the fourth face, and a firstdistance between the first face and the second face being larger than asecond distance between the third face and the fourth face, the secondelectrode being disposed between the second face and the firstsubstrate, looking from a direction from the first substrate toward thesecond substrate, the second reflective film, the first electrode, andthe second electrode overlapping to the first portion.
 2. The variablewavelength interference filter according to claim 1, the first substratehaving a third portion and a fourth portion, the fourth portion beingdisposed so as to surround the third portion, looking from a directionfrom the first substrate toward the second substrate, the first portionoverlapping to the third portion, the first electrode overlapping to thefourth portion.
 3. The variable wavelength interference filter accordingto claim 1, the second portion surrounding a circumference of the firstportion continuously.
 4. The variable wavelength interference filteraccording to claim 1, further comprising: a first film that decreasesbending of the second substrate, the first film and the secondreflective electrode being disposed so as to sandwich the first portion.5. The variable wavelength interference filter according to claim 1, thegap changing by changing applied voltage between the first electrode andthe second electrode.
 6. The variable wavelength interference filteraccording to claim 1, further comprising: a third electrode that isdisposed between the first substrate and the second substrate; and afourth electrode that is disposed between the third electrode and thesecond substrate, the first electrode being disposed between the firstreflective film and the third electrode, and the second electrode beingdisposed between the second reflective film and the fourth electrode. 7.The variable wavelength interference filter according to claim 1, thesecond portion being disposed between the first portion and a fifthportion of the second substrate, the fifth portion connecting to thefirst substrate via a first bonding film.
 8. A substrate of a variablewavelength interference filter comprising: a first substrate; a firstreflective film that is disposed at a first side of the first substrate;a first electrode that is disposed at the first side of the firstsubstrate; and the first substrate having a first portion and a secondportion, the second portion being disposed so as to surround the firstportion, the first portion having a first face and a second face, thesecond portion having a third face and a fourth face, the first facecontinuing to the third face, the first face being opposed to the secondface, the third face being opposed to the fourth face, and a firstdistance between the first face and the second face is larger than asecond distance between the third face and the fourth face, looking froma direction from the first substrate toward the first reflective film,the first reflective film and the first electrode overlapping the firstface.
 9. The substrate of a variable wavelength interference filteraccording to claim 8, further comprising: a first film that decreasesbending of the first substrate, the first film and the first reflectiveelectrode being disposed so as to sandwich the first portion.
 10. Anoptical module comprising: a variable wavelength interference filteraccording to claim
 1. 11. An optical analyzer comprising: a variablewavelength interference filter according to claim
 1. 12. A variablewavelength interference filter comprising: a first substrate; a secondsubstrate that faces the first substrate; a first reflective film thatis disposed between the first substrate and the second substrate; asecond reflective film that is disposed between the first reflectivefilm and the second substrate, a gap existing between the firstreflective film and the second reflective film; a first electrode thatis disposed between the first substrate and the second substrate; and asecond electrode that is disposed between the first electrode and thesecond substrate; wherein the second substrate has a first portion and asecond portion, the second portion is disposed so as to surround thefirst portion, the first portion has a first face and a second face, andthe second portion has a third face and the second face, the first faceis opposed to the first substrate and the second face, and a firstdistance between the first face and the second face is larger than asecond distance between the third face and the second face, the secondelectrode is disposed between the second face and the first substrate,and looking from a direction from the first substrate toward the secondsubstrate, the second reflective film, the first electrode, and thesecond electrode overlap the first portion.
 13. The variable wavelengthinterference filter according to claim 12, wherein, looking from adirection along the second surface, the second electrode overlaps thesecond reflective film.
 14. The variable wavelength interference filteraccording to claim 12, wherein the second face is disposed between thefirst face and the first substrate.
 15. The variable wavelengthinterference filter according to claim 12, wherein the first face isentirely co-planar with the third face.
 16. The variable wavelengthinterference filter according to claim 1, wherein the first face isentirely co-planar with the third face.
 17. The substrate of a variablewavelength interference filter according to claim 8, wherein the firstface is entirely co-planar with the third face.